I know I will get a lot of dislike for this, but please take your time to finish reading first, like I took mine to put out my thoughts here.
Let's face it. LL Cool J is chosen because he is famous, not because he is a standout actor or the writers actually have plans for him. Tell me at least three other adjectives that you can describe him besides "big", "black", or "brave". Those adjectives are pretty much what Sam is, which is not good at all, because that makes him a mere stock action sidekick hero to G. Compare him to Tony in the original. He is a capable gunfighter, epic prankster, funny womanizer, and, most of all, unbeatable annoyer. Only Tony can be annoying enough that the head of Mossad unwittingly leaks his own plan--while Eli was the one who interrogates him! What can Sam do? Fight? Well, so can G, Kensi, and Deeks, yes?
And Daniela Ruah's character. Kensi. She has no depth. Just like Sam, she is the token action girl every show needs to have nowadays. Why we love Ziva David? Because she is ex-Mossad assassin. Because she continuously mangles American idioms. Because she drives like crazy that even his father is scared. Because she dares to face the invincible Gibbs, match Tony's funny but witty charm, befriend the much-hazed McGee, and win Abby's trust. What is it in Kensi that besides kicking people's butt we still want to watch her? Her relationship with Deeks? Well, you see, their lines after Deeks saves him in Absolution: K: I need to pee. D: You already did. What! That is classless.
And Eric. All he's doing is being a tech geek. Not that it's bad, but compare him to Abby. That hyperactive Gothic girl follows absolutely no dress codes whatsoever, is addicted to caffeine drinks which would have killed her heart right now, and ignores all common etiquettes like blasting her music and hugging people around. But she's still in! Why? Because she's so good at what she's doing and we viewers love her for her freakiness! Besides wearing hawaii shirt, putting his feet on the table, and throwing failed dry humor, Eric is nobody to miss. Much less that new character, Nell Jones, ohh...we don't need more characters, we need less!
The argument rests.